How cardinals tell her songs from his

 A New York researcher has finally figured out how to distinguish a female cardinal's song from a male's, a feat that has challenged birdwatchers for years.

 The adult females whistle slightly more nasal songs than males do and show more variation from syllable to syllable, reports Ayako Yamaguchi of Columbia University. In the August Condor, she proposes that hormonal differences leave the adult females stuck with the avian equivalent of a teenage-boy voice.

 The female Northern cardinal may have the coloring of a muddy hiking boot, but she's remarkable as one of the few female birds to sing in the temperate zone. Females of many tropical species do sing, Yamaguchi points out, perhaps because keeping in touch with a mate can be so difficult in dense vegetation. Yamaguchi sees cardinals as essentially a tropical species, which spread north only during the last hundred years.

 A male and female cardinal sing the same types of songs, and to people, her version sounds very similar to his, Yamaguchi observes. Yet the birds know the difference. She has found that male cardinals attack speakers broadcasting a male song, and a female recording prompts females to sing.

 After listening to the songs for about a month, Yamaguchi thought of comparing their harmonics. Female versions have more overtones, creating a nasal sound much as bagpipe overtones do. Also, females do not repeat notes as precisely as males do.

 Yamaguchi rejects the idea that the females learn only from Mom and males just copy Dad. Thirty cardinals raised in captivity learned songs from recordings of both males and females, she reports. Yet, "if a girl learned a song from Daddy, she still made it sound feminine," Yamaguchi says. Likewise, males added guy traits to songs they picked up from a recorded female.

 Hormones might explain the song differences, Yamaguchi suggests. Young male cardinals go through a nasal, wobbly phase as their androgen kicks in. Females sing "as if they have a juvenile male song," Yamaguchi says.

 The idea intrigues J. Jordan Price of the University of North Carolina at Chapel Hill, who has studied male and female tropical birdsongs. "There may be a reason why [cardinal] females aren't developing," he says. They may use music close-up, chatting with mates or fussing at another female who dares to invade. Males, however, may face stronger pressure to evolve purer tones, which carry farther, to announce "no trespassing" or "seeking mate" to distant cardinals.